1. Field of the Invention
The present invention relates to a resist composition, a method of forming a resist pattern using the resist composition, a compound useful as an acid generator for the resist composition, and the acid generator.
Priority is claimed on Japanese Patent Application No. 2008-252212, filed Sep. 30, 2008, and Japanese Patent Application No. 2009-210857, filed Sep. 11, 2009, the content of which is incorporated herein by reference.
2. Description of Related Art
In lithography techniques, for example, a resist film composed of a resist material is formed on a support such as a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays, mass production of semiconductor elements using KrF excimer lasers and ArF excimer lasers has commenced. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beams, extreme ultraviolet radiation (EUV), and X rays.
Conventionally, negative resist materials for use in processes that use either i-line radiation or a KrF excimer laser (248 nm) as the light source have employed chemically amplified negative resist compositions containing a combination of an acid generator, an alkali-soluble resin such as a novolak resin or a polyhydroxystyrene, and an amino resin such as a melamine resin or urea resin (for example, refer to Patent Document 1).
Furthermore, negative resist materials that can be applied to processes that use an ArF excimer laser of even shorter wavelength (193 nm) use materials that exhibit improved transparency to ArF excimer lasers. For example, a negative resist composition that includes a resin component containing carboxyl groups, a cross-linking agent containing alcoholic hydroxyl groups, and an acid generator has been proposed.
In this composition, the carboxyl groups within the resin component react with the alcoholic hydroxyl groups within the cross-linking agent under the action of the acid generated from the acid generator. As a result, the resin component changes from an alkali-soluble state to an alkali-insoluble state.
Furthermore, negative resist compositions have also been proposed that include a resin component containing carboxyl groups or carboxylate ester groups as well as alcoholic hydroxyl groups, and an acid generator, wherein an intermolecular reaction between the carboxyl groups or carboxylate ester groups and the alcoholic hydroxyl groups within the resin component, under the action of the acid generated from the acid generator, causes the resin component to change from an alkali-soluble state to an alkali-insoluble state (for example, see Non-patent Documents 1 to 4 and Patent Document 2).
As acid generators usable in a chemically amplified resist composition, various types have been proposed including, for example, onium salt-based acid generators such as iodonium salts and sulfonium salts; oxime sulfonate-based acid generators; diazomethane-based acid generators; nitrobenzylsulfonate-based acid generators; iminosulfonate-based acid generators; and disulfone-based acid generators.
Currently, as acid generators, onium salt-based acid generators having an onium ion such as triphenylsulfonium as the cation moiety are used. As the anion moiety for onium salt-based acid generators, an alkylsulfonate ion or a fluorinated alkylsulfonate ion in which a part or all of the hydrogen atoms within the aforementioned alkylsulfonate ion has been substituted with fluorine atoms is typically used (for example, refer to Patent Document 3).
In those cases where such onium salt-based acid generators are used, it is considered that length of the alkyl group or fluorinated alkyl group within the anion moiety is preferably long, as diffusion of acid within a resist film after exposure can be suppressed. However, an alkyl group or fluorinated alkyl group having 6 or more carbon atoms is hardly decomposable, and hence, in consideration of safety in handling in terms of bioaccumulation, those having 4 or less carbon atoms, for example, a nonafluorobutanesulfonic acid ion or the like are used.    [Patent Document 1] Japanese Examined Patent Application, Second Publication No. Hei 8-3635    [Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2000-206694    [Patent Document 3] Japanese Unexamined Patent Application, First Publication No. 2005-37888    [Non-Patent Document 1]J. Photopolym. Sci. Tech., Vol. 10, No. 4, pages 579 to 584 (1997)    [Non-Patent Document 2]J. Photopolym. Sci. Tech., Vol. 11, No. 3, pages 507 to 512 (1998)    [Non-Patent Document 3] SPIE Advances in Resist Technology and Processing XIV, Vol. 3333, pages 417 to 424 (1998)    [Non-Patent Document 4] SPIE Advances in Resist Technology and Processing XIX, Vol. 4690, pages 94 to 100 (2002)
In recent years, as requirements for high resolution increase with progress in the miniaturization of resist patterns, improvement in various lithography properties has been demanded. Further, associated with this trend, development of novel resist materials has been desired.
As the cation for onium salt-based acid generators that have been conventionally used in resist materials, for example, cations such as triphenylsulfonium have typically been used. Because the cations exhibit relatively high hydrophobicity, it is presumed that onium salt-based acid generators having such cations are excellent in terms of compatibility with the base components of resists and the solubility in an organic solvent, and are thus contributing to the improvements in lithography properties.
However, the solubility of acid generators in an alkali developing solution tends to deteriorate as the hydrophobicity increases. When the solubility of an acid generator in an alkali developing solution deteriorates, the acid generator does not dissolve satisfactorily at the time of development, which may cause problems such as the occurrence of defects and the footing of resist patterns. The term “defects” refers to general abnormalities of a resist pattern, which are detected when observed from right above the developed resist pattern, using, for example, a surface defect detection apparatus (trade name: “KLA”) manufactured by KLA-TENCOR Corporation. Examples of these abnormalities include post-developing scum, foam, dust, bridges across different portions of the resist pattern, color irregularities, and foreign deposits.
Therefore, development of a novel compound which can achieve both excellent solubility in developing solutions and satisfactory lithography properties and which is more useful as an acid generator for a resist composition has been demanded.
The present invention takes the above circumstances into consideration, with an object of providing a novel compound useful as an acid generator for a resist composition, an acid generator including the compound, a resist composition containing the acid generator, and a method of forming a resist pattern that uses the resist composition.